ME. H. F. BLANFOED ON THE WINDS OF NOETHEEN INDIA. 
605 
lasts throughout the rains, and has a marked influence on the winds. The seat of lowest 
pressure lies, however, in the direction of the Punjab and the desert of Bikaneer. 
Finally, in September and October the pressure increases more rapidly, and in such 
measure as to become nearly equalized, prior to the very different distribution which 
ushers in the cold season and its northerly winds. 
It is evident, on inspection of the charts, that the distribution of pressure, to a certain 
extent, follows that of temperature near the ground surface, in an inverse ratio of 
intensity. Thus (omitting from consideration the Punjab and Upper Assam, for which 
barometric data are wanting) Benares is in the cold weather the seat of highest pres- 
sure and also of lowest abnormal temperature*. The ridge of high pressure of which 
this is the culminating point, and which extends in a curve from Roorkee to Cuttack f, 
is in like manner evidently coincident with the southward bend of the isothermals 
shown in the cold-weather charts from November to February, especially the first of these 
months ; and, on the other hand, the relatively low pressure of the delta coincides with 
the northward bend of the isothermals. In these cases, then, there is an apparent coin- 
cidence of the isobaric with the isabnormal rather than the isothermal curves. But in 
the hot-weather months, although a similar coincidence is still traceable, the infusion 
of water-vapour, which tends to equalize the temperature at higher levels with that near 
the ground J, is evidently influential. The trough of low pressure in April between 
Berhampore and Nagpore has along its axis a temperature not much below 90° when 
reduced to sea-level, and probably a vapour-tension higher than any part of the region 
to the north-west. That of Nagpore, e. g., is 0'504 inch, and that of Jubbulpore only 
0 - 398 ; that of Hazareebagh does not indeed seem so high as that of Patna and Benares ; 
but it would appear from the Table at page 596 that the vapour-tension in the hot- 
weather months diminishes very rapidly in the first few thousand feet of the atmosphere ; 
and although I think it probable that, owing to the high temperature of the ground 
surface of the plateau, the humidity of Hazareebagh is lower than that of the free 
atmosphere at the same elevation, there is no reason to believe that the vapour-tension 
is very much influenced by this cause, since there is no evaporating surface. If the 
vapour-tension of Hazareebagh and Patna in April be compared with that of the same 
stations in January, the rise at Hazareebagh is seen to be proportionally greater than 
at Patna ; and at all stations to the south and east of Hazareebagh the relative rise 
very greatly exceeds that of stations to the north and west. 
I infer, therefore, that while the temperature of Hazareebagh near the ground 
level in April is but little lower than that of the delta (nearly 2000 feet nearer the 
sea-level) and of Patna (which is more than 1700 feet lower), the admixture of water- 
vapour, though less than over the former, is probably greater than at the same eleva- 
tion over the latter and all places to the west and north-west ; that a higher tempe- 
rature is thus imparted to the still more elevated strata of the atmosphere, the result 
being to render their mean density somewhat lower than over either. The temperatures 
* The term abnormal is used in the sense given to it by M. Dove. 
f See preceding page. J See ante, page 591. 
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